Three new furanosesterterpene tetronic
acids, sulawesins A–C
(<b>1</b>–<b>3</b>), were isolated from a <i>Psammocinia</i> sp. marine sponge, along with the known compounds
ircinins-1 (<b>4</b>) and -2 (<b>5</b>). Although ircinins-1
and -2 were previously isolated as (+)- or (−)-enantiomers
from marine sponges, we isolated them as enantiomeric mixtures. Sulawesins
A and B possess a new carbon skeleton with a 5-(furan-3-yl)-4-hydroxycyclopent-2-enone
moiety and were also found to be diastereomeric mixtures of four isomers
by an HPLC analysis with a chiral-phase column. Sulawesin C has a
dimeric structure of ircinin-1 and is the first dimer in this family.
USP7, a deubiquitinating enzyme, is an emergent target of cancer therapy,
and the isolated compounds inhibited USP7 with IC<sub>50</sub> values
in the range of 2.7–4.6 μM.